Thermal regulation of balloon payload using electronic ink

ABSTRACT

A balloon payload is provided having a payload structure, an outer surface of the payload structure comprised of an electronic ink covering, and a control system configured to change the electronic ink covering from a first state having first energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, to a second state having second energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, wherein the second energy absorptive properties allow less thermal energy to enter the payload than the first energy absorptive properties.

BACKGROUND

Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.

Computing devices such as personal computers, laptop computers, tablet computers, cellular phones, and countless types of Internet-capable devices are increasingly prevalent in numerous aspects of modern life. As such, the demand for data connectivity via the Internet, cellular data networks, and other such networks, is growing. However, there are many areas of the world where data connectivity is still unavailable, or if available, is unreliable and/or costly. Accordingly, additional network infrastructure is desirable.

SUMMARY

In one aspect, a balloon payload is provided having a payload structure, an outer surface of the payload structure comprised of an electronic ink covering, and a control system configured to change the electronic ink covering from a first state having first energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, to a second state having second energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, wherein the second energy absorptive properties allow less thermal energy to enter the payload than the first energy absorptive properties.

In another aspect, a computer-implemented method is provided, comprising the steps of causing a payload of a balloon to be placed in a first state wherein the payload includes a payload structure where the outer surface of the payload is comprised of an electronic ink covering, where in the first state, the electronic ink covering has first energy absorptive properties with respect to the thermal energy that enters the payload through the electronic ink covering, and causing the payload of the balloon to change to a second state, where in the second state, the electronic ink covering has second energy absorptive properties that allow less thermal energy to enter the payload than when the electronic ink covering is in the first state. The method may also include causing the payload to change back to the first state.

In another aspect, a non-transitory computer readable medium has stored therein instructions that are executable by a computing device to cause the computing device to perform functions comprising causing a payload of a balloon to be placed in a first state wherein the payload includes a payload structure where the outer surface of the payload is comprised of an electronic ink covering, where in the first state, the electronic ink covering has first energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, and causing the payload of the balloon to change to a second state, where in the second state, the electronic ink covering has second energy absorptive properties that allow less thermal energy to enter the payload through the electronic ink covering than when the electronic ink covering is in the first state.

These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram illustrating a balloon network, according to an example embodiment.

FIG. 2 is a block diagram illustrating a balloon-network control system, according to an example embodiment.

FIG. 3 is a simplified block diagram illustrating a high-altitude balloon, according to an example embodiment.

FIG. 4 shows a balloon network that includes super-nodes and sub-nodes, according to an example embodiment.

FIG. 5 shows a balloon with a payload in a first energy absorptive state, according to an example embodiment.

FIG. 6 shows the balloon and payload of FIG. 5, with the payload in a second energy absorptive state, according to an example embodiment.

FIG. 7A shows a cross-section of the payload of FIG. 5 taken along the lines 7A-7A.

FIG. 7B shows a cross-section of the payload of FIG. 6 taken along the lines 7B-7B.

FIG. 8A shows an enlarged view of encircled portion 8A shown in FIG. 7A.

FIG. 8B shows an enlarged view of the encircled portion 8B shown in FIG. 7B.

FIG. 9 shows an enlarged view of an electronic ink covering on a payload with a potential applied across the electrodes, according to an example embodiment.

FIG. 10 shows an enlarged view of the electronic ink covering of FIG. 9 without a potential applied across the electrodes.

FIG. 11 is a method, according to an example embodiment.

DETAILED DESCRIPTION

Example methods and systems are described herein. Any example embodiment or feature described herein is not necessarily to be construed as preferred or advantageous over other embodiments or features. The example embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.

Furthermore, the particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an example embodiment may include elements that are not illustrated in the Figures.

1. Overview

Example embodiments help to provide a data network that includes a plurality of balloons; for example, a mesh network formed by high-altitude balloons deployed in the stratosphere. Since winds in the stratosphere may affect the locations of the balloons in a differential manner, each balloon in an example network may be configured to change its horizontal position by adjusting its vertical position (i.e., altitude). For instance, by adjusting its altitude, a balloon may be able find winds that will carry it horizontally (e.g., latitudinally and/or longitudinally) to a desired horizontal location.

Further, in an example balloon network, the balloons may communicate with one another using free-space optical communications. For instance, the balloons may be configured for optical communications using lasers and/or ultra-bright LEDs (which are also referred to as “high-power” or “high-output” LEDs). In addition, the balloons may communicate with ground-based station(s) using radio-frequency (RF) communications.

In some embodiments, a high-altitude-balloon network may be homogenous. That is, the balloons in a high-altitude-balloon network could be substantially similar to each other in one or more ways. More specifically, in a homogenous high-altitude-balloon network, each balloon is configured to communicate with one or more other balloons via free-space optical links. Further, some or all of the balloons in such a network, may additionally be configured to communicate with ground-based and/or satellite-based station(s) using RF and/or optical communications. Thus, in some embodiments, the balloons may be homogenous in so far as each balloon is configured for free-space optical communication with other balloons, but heterogeneous with regard to RF communications with ground-based stations.

In other embodiments, a high-altitude-balloon network may be heterogeneous, and thus may include two or more different types of balloons. For example, some balloons in a heterogeneous network may be configured as super-nodes, while other balloons may be configured as sub-nodes. It is also possible that some balloons in a heterogeneous network may be configured to function as both a super-node and a sub-node. Such balloons may function as either a super-node or a sub-node at a particular time, or, alternatively, act as both simultaneously depending on the context. For instance, an example balloon could aggregate search requests of a first type to transmit to a ground-based station. The example balloon could also send search requests of a second type to another balloon, which could act as a super-node in that context. Further, some balloons, which may be super-nodes in an example embodiment, can be configured to communicate via optical links with ground-based stations and/or satellites.

In an example configuration, the super-node balloons may be configured to communicate with nearby super-node balloons via free-space optical links. However, the sub-node balloons may not be configured for free-space optical communication, and may instead be configured for some other type of communication, such as RF communications. In that case, a super-node may be further configured to communicate with sub-nodes using RF communications. Thus, the sub-nodes may relay communications between the super-nodes and one or more ground-based stations using RF communications. In this way, the super-nodes may collectively function as backhaul for the balloon network, while the sub-nodes function to relay communications from the super-nodes to ground-based stations.

During the course of a 24 hour day, a balloon can experience a wide environmental temperature range. For example, at high altitudes, the external night time temperatures may be extremely cold, and during the day time, under intense sunlight, the temperature may be much higher. Typically, the payload of a balloon includes a number of instruments and electronic devices. The wide environmental temperature range may be undesirable for the instruments and electronic devices located in the payload of the balloon. Therefore, it is desirable, if possible, to provide a more narrow temperature range for the payload, and the equipment positioned therein. Thus, when the sun is at its brightest, the temperature of the payload may be effectively lowered by reducing the amount of sunlight allowed to reach the payload of the balloon, which may be accomplished by providing a reflective surface on the payload, or a light-colored or white covering on the payload that does not absorb the sunlight.

However, near the end of the day, as the sun goes down, and less sunlight is directed toward the balloon, it may be desirable to direct as much sunlight as possible into the payload. Thus, when the sunlight is low, the temperature of the payload may be effectively increased by allowing sunlight to enter the payload and heat the instruments and electronic devices within the payload, which may be accomplished by providing an energy absorptive surface on the payload, such as a dark-colored or black surface, and/or a transparent covering on the payload, that will allow the heat from the sunlight to be transferred into the payload.

Thus, in some circumstances it may be desirable to provide a payload having a reflective surface, or less energy absorptive surface, such as a light-colored, or white surface, while other times it may be desirable to provide a payload having an energy absorptive surface, such as a dark-colored, or black surface. Therefore, it may be desirable to have a payload that is capable of having the surface of the payload change from one having a reflective surface, or less energy absorptive surface, such as light-colored, or white surface, to one having an energy absorptive surface, such as a dark-colored, or black surface.

Example embodiments disclose a payload that has a surface that may change from a first, relatively high energy absorptive surface to a second, lower energy absorptive surface. For example, the surface of the payload may be covered with an electronic ink covering that may be changed from a dark-colored, energy absorptive surface, to a light-colored, less energy absorptive surface by applying a potential difference across electrodes associated with the electronic ink covering on the payload. The electronic ink covering may have a first state where the surface is a dark-colored, energy absorptive surface, and a second state where the surface is a light-colored, energy reflective surface.

The term “electronic ink” is a term used broadly herein and covers electrophoretic displays, as well as any other composition or product that is capable of changing its energy absorptive properties when a potential is applied across electrodes associated with that composition or product. Thus, the electronic ink may include a dielectric fluid and a suspension of particles that visually contrast with the dielectric fluid, wherein when a potential difference is applied between two electrodes, the particles are caused to migrate towards one of the electrodes. The dielectric fluid and suspension of particles may be positioned within microcapsules that are positioned between the electrodes.

Thus, the payload may be designed to serve as a solar thermal energy collection system. When it is desired to obtain or collect more solar thermal energy in the payload, the payload may have an absorptive surface, such a dark-colored, or black surface, and/or a transparent covering, and where less solar thermal energy is desired for the payload, reflective or a light-colored, or white surface may be provided on the payload that allows for less transmission or absorption of solar energy within the payload. It should also be noted that the surface of the payload might look very different in the thermal IR vs. the visible band. Thus, it may be useful to characterize or describe the surface of the payload in terms of its reflectivity, transmissivity, and emissivity properties in the two bands (thermal IR and visible band) because the properties may be quite different. For example, envelope material that looks white to human eyes might in fact be quite black (low R (reflectivity), high E (emissivity), low T (transmissivity) when viewed in the thermal IR. Likewise, a material that appears very reflective (high R) when viewed in the visible band may have very different properties when viewed in the thermal IR band.

Furthermore, the payload may include one or more solar cells to store energy that can be used for powering the electronic ink covering used on the surface of the payload. For example, solar energy stored during the day may be used to change the surface of the payload from an energy absorptive surface to an energy reflective surface, and vice versa.

2. Example Balloon Networks

FIG. 1 is a simplified block diagram illustrating a balloon network 100, according to an example embodiment. As shown, balloon network 100 includes balloons 102A to 102F, which are configured to communicate with one another via free-space optical links 104. Balloons 102A to 102F could additionally or alternatively be configured to communicate with one another via RF links 114. Balloons 102A to 102F may collectively function as a mesh network for packet-data communications. Further, at least some of balloons 102A and 102B may be configured for RF communications with ground-based stations 106 and 112 via respective RF links 108. Further, some balloons, such as balloon 102F, could be configured to communicate via optical link 110 with ground-based station 112.

In an example embodiment, balloons 102A to 102F are high-altitude balloons, which are deployed in the stratosphere. At moderate latitudes, the stratosphere includes altitudes between approximately 10 kilometers (km) and 50 km altitude above the surface. At the poles, the stratosphere starts at an altitude of approximately 8 km. In an example embodiment, high-altitude balloons may be generally configured to operate in an altitude range within the stratosphere that has relatively low wind speed (e.g., between 5 and 20 miles per hour (mph)).

More specifically, in a high-altitude-balloon network, balloons 102A to 102F may generally be configured to operate at altitudes between 18 km and 25 km (although other altitudes are possible). This altitude range may be advantageous for several reasons. In particular, this layer of the stratosphere generally has relatively low wind speeds (e.g., winds between 5 and 20 mph) and relatively little turbulence. Further, while the winds between 18 km and 25 km may vary with latitude and by season, the variations can be modeled in a reasonably accurate manner. Additionally, altitudes above 18 km are typically above the maximum flight level designated for commercial air traffic. Therefore, interference with commercial flights is not a concern when balloons are deployed between 18 km and 25 km.

To transmit data to another balloon, a given balloon 102A to 102F may be configured to transmit an optical signal via an optical link 104. In an example embodiment, a given balloon 102A to 102F may use one or more high-power light-emitting diodes (LEDs) to transmit an optical signal. Alternatively, some or all of balloons 102A to 102F may include laser systems for free-space optical communications over optical links 104. Other types of free-space optical communication are possible. Further, in order to receive an optical signal from another balloon via an optical link 104, a given balloon 102A to 102F may include one or more optical receivers. Additional details of example balloons are discussed in greater detail below, with reference to FIG. 3.

In a further aspect, balloons 102A to 102F may utilize one or more of various different RF air-interface protocols for communication with ground-based stations 106 and 112 via respective RF links 108. For instance, some or all of balloons 102A to 102F may be configured to communicate with ground-based stations 106 and 112 using protocols described in IEEE 802.11 (including any of the IEEE 802.11 revisions), various cellular protocols such as GSM, CDMA, UMTS, EV-DO, WiMAX, and/or LTE, and/or one or more propriety protocols developed for balloon-ground RF communication, among other possibilities.

In a further aspect, there may be scenarios where RF links 108 do not provide a desired link capacity for balloon-to-ground communications. For instance, increased capacity may be desirable to provide backhaul links from a ground-based gateway, and in other scenarios as well. Accordingly, an example network may also include downlink balloons, which could provide a high-capacity air-ground link.

For example, in balloon network 100, balloon 102F is configured as a downlink balloon. Like other balloons in an example network, a downlink balloon 102F may be operable for optical communication with other balloons via optical links 104. However, a downlink balloon 102F may also be configured for free-space optical communication with a ground-based station 112 via an optical link 110. Optical link 110 may therefore serve as a high-capacity link (as compared to an RF link 108) between the balloon network 100 and the ground-based station 112.

Note that in some implementations, a downlink balloon 102F may additionally be operable for RF communication with ground-based stations 106. In other cases, a downlink balloon 102F may only use an optical link for balloon-to-ground communications. Further, while the arrangement shown in FIG. 1 includes just one downlink balloon 102F, an example balloon network can also include multiple downlink balloons. On the other hand, a balloon network can also be implemented without any downlink balloons.

In other implementations, a downlink balloon may be equipped with a specialized, high-bandwidth RF communication system for balloon-to-ground communications, instead of, or in addition to, a free-space optical communication system. The high-bandwidth RF communication system may take the form of an ultra-wideband system, which may provide an RF link with substantially the same capacity as one of the optical links 104. Other forms are also possible.

Ground-based stations, such as ground-based stations 106 and/or 112, may take various forms. Generally, a ground-based station may include components such as transceivers, transmitters, and/or receivers for communication via RF links and/or optical links with a balloon network. Further, a ground-based station may use various air-interface protocols in order to communicate with a balloon 102A to 102F over an RF link 108. As such, ground-based stations 106 and 112 may be configured as an access point via which various devices can connect to balloon network 100. Ground-based stations 106 and 112 may have other configurations and/or serve other purposes without departing from the scope of the invention.

In a further aspect, some or all of balloons 102A to 102F could be configured to establish a communication link with space-based satellites in addition to, or as an alternative to, a ground-based communication link. In some embodiments, a balloon may communicate with a satellite via an optical link. However, other types of satellite communications are possible.

Further, some ground-based stations, such as ground-based stations 106 and 112, may be configured as gateways between balloon network 100 and one or more other networks. Such ground-based stations 106 and 112 may thus serve as an interface between the balloon network and the Internet, a cellular service provider's network, and/or other types of networks. Variations on this configuration and other configurations of ground-based stations 106 and 112 are also possible.

2a) Mesh Network Functionality

As noted, balloons 102A to 102F may collectively function as a mesh network. More specifically, since balloons 102A to 102F may communicate with one another using free-space optical links, the balloons may collectively function as a free-space optical mesh network.

In a mesh-network configuration, each balloon 102A to 102F may function as a node of the mesh network, which is operable to receive data directed to it and to route data to other balloons. As such, data may be routed from a source balloon to a destination balloon by determining an appropriate sequence of optical links between the source balloon and the destination balloon. These optical links may be collectively referred to as a “lightpath” for the connection between the source and destination balloons. Further, each of the optical links may be referred to as a “hop” on the lightpath.

To operate as a mesh network, balloons 102A to 102F may employ various routing techniques and self-healing algorithms. In some embodiments, a balloon network 100 may employ adaptive or dynamic routing, where a lightpath between a source and destination balloon is determined and set-up when the connection is needed, and released at a later time. Further, when adaptive routing is used, the lightpath may be determined dynamically depending upon the current state, past state, and/or predicted state of the balloon network.

In addition, the network topology may change as the balloons 102A to 102F move relative to one another and/or relative to the ground. Accordingly, an example balloon network 100 may apply a mesh protocol to update the state of the network as the topology of the network changes. For example, to address the mobility of the balloons 102A to 102F, balloon network 100 may employ and/or adapt various techniques that are employed in mobile ad hoc networks (MANETs). Other examples are possible as well.

In some implementations, a balloon network 100 may be configured as a transparent mesh network. More specifically, in a transparent balloon network, the balloons may include components for physical switching that is entirely optical, without any electrical components involved in the physical routing of optical signals. Thus, in a transparent configuration with optical switching, signals travel through a multi-hop lightpath that is entirely optical.

In other implementations, the balloon network 100 may implement a free-space optical mesh network that is opaque. In an opaque configuration, some or all balloons 102A to 102F may implement optical-electrical-optical (OEO) switching. For example, some or all balloons may include optical cross-connects (OXCs) for OEO conversion of optical signals. Other opaque configurations are also possible. Additionally, network configurations are possible that include routing paths with both transparent and opaque sections.

In a further aspect, balloons in an example balloon network 100 may implement wavelength division multiplexing (WDM), which may help to increase link capacity. When WDM is implemented with transparent switching, physical lightpaths through the balloon network may be subject to the “wavelength continuity constraint.” More specifically, because the switching in a transparent network is entirely optical, it may be necessary to assign the same wavelength for all optical links on a given lightpath.

An opaque configuration, on the other hand, may avoid the wavelength continuity constraint. In particular, balloons in an opaque balloon network may include the OEO switching systems operable for wavelength conversion. As a result, balloons can convert the wavelength of an optical signal at each hop along a lightpath. Alternatively, optical wavelength conversion could take place at only selected hops along the lightpath.

Further, various routing algorithms may be employed in an opaque configuration. For example, to determine a primary lightpath and/or one or more diverse backup lightpaths for a given connection, example balloons may apply or consider shortest-path routing techniques such as Dijkstra's algorithm and k-shortest path, and/or edge and node-diverse or disjoint routing such as Suurballe's algorithm, among others. Additionally or alternatively, techniques for maintaining a particular quality of service (QoS) may be employed when determining a lightpath. Other techniques are also possible.

2b) Station-Keeping Functionality

In an example embodiment, a balloon network 100 may implement station-keeping functions to help provide a desired network topology. For example, station-keeping may involve each balloon 102A to 102F maintaining and/or moving into a certain position relative to one or more other balloons in the network (and possibly in a certain position relative to the ground). As part of this process, each balloon 102A to 102F may implement station-keeping functions to determine its desired positioning within the desired topology, and if necessary, to determine how to move to the desired position.

The desired topology may vary depending upon the particular implementation. In some cases, balloons may implement station-keeping to provide a substantially uniform topology. In such cases, a given balloon 102A to 102F may implement station-keeping functions to position itself at substantially the same distance (or within a certain range of distances) from adjacent balloons in the balloon network 100.

In other cases, a balloon network 100 may have a non-uniform topology. For instance, example embodiments may involve topologies where balloons are distributed more or less densely in certain areas, for various reasons. As an example, to help meet the higher bandwidth demands that are typical in urban areas, balloons may be clustered more densely over urban areas. For similar reasons, the distribution of balloons may be denser over land than over large bodies of water. Many other examples of non-uniform topologies are possible.

In a further aspect, the topology of an example balloon network may be adaptable. In particular, station-keeping functionality of example balloons may allow the balloons to adjust their respective positioning in accordance with a change in the desired topology of the network. For example, one or more balloons could move to new positions to increase or decrease the density of balloons in a given area. Other examples are possible.

In some embodiments, a balloon network 100 may employ an energy function to determine if and/or how balloons should move to provide a desired topology. In particular, the state of a given balloon and the states of some or all nearby balloons may be input to an energy function. The energy function may apply the current states of the given balloon and the nearby balloons to a desired network state (e.g., a state corresponding to the desired topology). A vector indicating a desired movement of the given balloon may then be determined by determining the gradient of the energy function. The given balloon may then determine appropriate actions to take in order to effectuate the desired movement. For example, a balloon may determine an altitude adjustment or adjustments such that winds will move the balloon in the desired manner.

2c) Control of Balloons in a Balloon Network

In some embodiments, mesh networking and/or station-keeping functions may be centralized. For example, FIG. 2 is a block diagram illustrating a balloon-network control system, according to an example embodiment. In particular, FIG. 2 shows a distributed control system, which includes a central control system 200 and a number of regional control-systems 202A to 202B. Such a control system may be configured to coordinate certain functionality for balloon network 204, and as such, may be configured to control and/or coordinate certain functions for balloons 206A to 206I.

In the illustrated embodiment, central control system 200 may be configured to communicate with balloons 206A to 206I via a number of regional control systems 202A to 202C. These regional control systems 202A to 202C may be configured to receive communications and/or aggregate data from balloons in the respective geographic areas that they cover, and to relay the communications and/or data to central control system 200. Further, regional control systems 202A to 202C may be configured to route communications from central control system 200 to the balloons in their respective geographic areas. For instance, as shown in FIG. 2, regional control system 202A may relay communications and/or data between balloons 206A to 206C and central control system 200, regional control system 202B may relay communications and/or data between balloons 206D to 206F and central control system 200, and regional control system 202C may relay communications and/or data between balloons 206G to 206I and central control system 200.

In order to facilitate communications between the central control system 200 and balloons 206A to 206I, certain balloons may be configured as downlink balloons, which are operable to communicate with regional control systems 202A to 202C. Accordingly, each regional control system 202A to 202C may be configured to communicate with the downlink balloon or balloons in the respective geographic area it covers. For example, in the illustrated embodiment, balloons 206A, 206F, and 206I are configured as downlink balloons. As such, regional control systems 202A to 202C may respectively communicate with balloons 206A, 206F, and 206I via optical links 206, 208, and 210, respectively.

In the illustrated configuration, only some of balloons 206A to 206I are configured as downlink balloons. The balloons 206A, 206F, and 206I that are configured as downlink balloons may relay communications from central control system 200 to other balloons in the balloon network, such as balloons 206B to 206E, 206G, and 206H. However, it should be understood that in some implementations, it is possible that all balloons may function as downlink balloons. Further, while FIG. 2 shows multiple balloons configured as downlink balloons, it is also possible for a balloon network to include only one downlink balloon, or possibly even no downlink balloons.

Note that a regional control system 202A to 202C may in fact just be a particular type of ground-based station that is configured to communicate with downlink balloons (e.g., such as ground-based station 112 of FIG. 1). Thus, while not shown in FIG. 2, a control system may be implemented in conjunction with other types of ground-based stations (e.g., access points, gateways, etc.).

In a centralized control arrangement, such as that shown in FIG. 2, the central control system 200 (and possibly regional control systems 202A to 202C as well) may coordinate certain mesh-networking functions for balloon network 204. For example, balloons 206A to 206I may send the central control system 200 certain state information, which the central control system 200 may utilize to determine the state of balloon network 204. The state information from a given balloon may include location data, optical-link information (e.g., the identity of other balloons with which the balloon has established an optical link, the bandwidth of the link, wavelength usage and/or availability on a link, etc.), wind data collected by the balloon, and/or other types of information. Accordingly, the central control system 200 may aggregate state information from some or all of the balloons 206A to 206I in order to determine an overall state of the network.

The overall state of the network may then be used to coordinate and/or facilitate certain mesh-networking functions such as determining lightpaths for connections. For example, the central control system 200 may determine a current topology based on the aggregate state information from some or all of the balloons 206A to 206I. The topology may provide a picture of the current optical links that are available in balloon network and/or the wavelength availability on the links. This topology may then be sent to some or all of the balloons so that a routing technique may be employed to select appropriate lightpaths (and possibly backup lightpaths) for communications through the balloon network 204.

In a further aspect, the central control system 200 (and possibly regional control systems 202A to 202C as well) may also coordinate certain station-keeping functions for balloon network 204. For example, the central control system 200 may input state information that is received from balloons 206A to 206I to an energy function, which may effectively compare the current topology of the network to a desired topology, and provide a vector indicating a direction of movement (if any) for each balloon, such that the balloons can move towards the desired topology. Further, the central control system 200 may use altitudinal wind data to determine respective altitude adjustments that may be initiated to achieve the movement towards the desired topology. The central control system 200 may provide and/or support other station-keeping functions as well.

FIG. 2 shows a distributed arrangement that provides centralized control, with regional control systems 202A to 202C coordinating communications between a central control system 200 and a balloon network 204. Such an arrangement may be useful to provide centralized control for a balloon network that covers a large geographic area. In some embodiments, a distributed arrangement may even support a global balloon network that provides coverage everywhere on earth. Of course, a distributed-control arrangement may be useful in other scenarios as well.

Further, it should be understood that other control-system arrangements are also possible. For instance, some implementations may involve a centralized control system with additional layers (e.g., sub-region systems within the regional control systems, and so on). Alternatively, control functions may be provided by a single, centralized, control system, which communicates directly with one or more downlink balloons.

In some embodiments, control and coordination of a balloon network may be shared by a ground-based control system and a balloon network to varying degrees, depending upon the implementation. In fact, in some embodiments, there may be no ground-based control systems. In such an embodiment, all network control and coordination functions may be implemented by the balloon network itself. For example, certain balloons may be configured to provide the same or similar functions as central control system 200 and/or regional control systems 202A to 202C. Other examples are also possible.

Furthermore, control and/or coordination of a balloon network may be de-centralized. For example, each balloon may relay state information to, and receive state information from, some or all nearby balloons. Further, each balloon may relay state information that it receives from a nearby balloon to some or all nearby balloons. When all balloons do so, each balloon may be able to individually determine the state of the network. Alternatively, certain balloons may be designated to aggregate state information for a given portion of the network. These balloons may then coordinate with one another to determine the overall state of the network.

Further, in some aspects, control of a balloon network may be partially or entirely localized, such that it is not dependent on the overall state of the network. For example, individual balloons may implement station-keeping functions that only consider nearby balloons. In particular, each balloon may implement an energy function that takes into account its own state and the states of nearby balloons. The energy function may be used to maintain and/or move to a desired position with respect to the nearby balloons, without necessarily considering the desired topology of the network as a whole. However, when each balloon implements such an energy function for station-keeping, the balloon network as a whole may maintain and/or move towards the desired topology.

As an example, each balloon A may receive distance information d₁ to d_(k) with respect to each of its k closest neighbors. Each balloon A may treat the distance to each of the k balloons as a virtual spring with vector representing a force direction from the first nearest neighbor balloon i toward balloon A and with force magnitude proportional to d_(i). The balloon A may sum each of the k vectors and the summed vector is the vector of desired movement for balloon A. Balloon A may attempt to achieve the desired movement by controlling its altitude.

Alternatively, this process could assign the force magnitude of each of these virtual forces equal to d_(i)×d_(i), for instance. Other algorithms for assigning force magnitudes for respective balloons in a mesh network are possible.

In another embodiment, a similar process could be carried out for each of the k balloons and each balloon could transmit its planned movement vector to its local neighbors. Further rounds of refinement to each balloon's planned movement vector can be made based on the corresponding planned movement vectors of its neighbors. It will be evident to those skilled in the art that other algorithms could be implemented in a balloon network in an effort to maintain a set of balloon spacings and/or a specific network capacity level over a given geographic location.

2d) Example Balloon Configuration

Various types of balloon systems may be incorporated in an example balloon network. As noted above, an example embodiment may utilize high-altitude balloons, which could typically operate in an altitude range between 18 km and 25 km. FIG. 3 shows a high-altitude balloon 300, according to an example embodiment. As shown, the balloon 300 includes an envelope 302, a skirt 304, a payload 306, and a cut-down system 308, which is attached between the balloon 302 and payload 304.

The envelope 302 and skirt 304 may take various forms, which may be currently well-known or yet to be developed. For instance, the envelope 302 and/or skirt 304 may be made of materials including metalized Mylar or BoPet. Additionally or alternatively, some or all of the envelope 302 and/or skirt 304 may be constructed from a highly-flexible latex material or a rubber material such as chloroprene. Other materials are also possible. Further, the shape and size of the envelope 302 and skirt 304 may vary depending upon the particular implementation. Additionally, the envelope 302 may be filled with various different types of gases, such as helium and/or hydrogen. Other types of gases are possible as well.

The payload 306 of balloon 300 may include a processor 312 and on-board data storage, such as memory 314. The memory 314 may take the form of or include a non-transitory computer-readable medium. The non-transitory computer-readable medium may have instructions stored thereon, which can be accessed and executed by the processor 312 in order to carry out the balloon functions described herein. Thus, processor 312, in conjunction with instructions stored in memory 314, and/or other components, may function as a controller of balloon 300.

The payload 306 of balloon 300 may also include various other types of equipment and systems to provide a number of different functions. For example, payload 306 may include an optical communication system 316, which may transmit optical signals via an ultra-bright LED system 320, and which may receive optical signals via an optical-communication receiver 322 (e.g., a photodiode receiver system). Further, payload 306 may include an RF communication system 318, which may transmit and/or receive RF communications via an antenna system 340.

The payload 306 may also include a power supply 326 to supply power to the various components of balloon 300. The power supply 326 could include a rechargeable battery. In other embodiments, the power supply 326 may additionally or alternatively represent other means known in the art for producing power. In addition, the balloon 300 may include a solar power generation system 327. The solar power generation system 327 may include solar panels and could be used to generate power that charges and/or is distributed by the power supply 326.

The payload 306 may additionally include a positioning system 324. The positioning system 324 could include, for example, a global positioning system (GPS), an inertial navigation system, and/or a star-tracking system. The positioning system 324 may additionally or alternatively include various motion sensors (e.g., accelerometers, magnetometers, gyroscopes, and/or compasses).

The positioning system 324 may additionally or alternatively include one or more video and/or still cameras, and/or various sensors for capturing environmental data.

Some or all of the components and systems within payload 306 may be implemented in a radiosonde or other probe, which may be operable to measure, e.g., pressure, altitude, geographical position (latitude and longitude), temperature, relative humidity, and/or wind speed and/or wind direction, among other information.

As noted, balloon 300 includes an ultra-bright LED system 320 for free-space optical communication with other balloons. As such, optical communication system 316 may be configured to transmit a free-space optical signal by modulating the ultra-bright LED system 320. The optical communication system 316 may be implemented with mechanical systems and/or with hardware, firmware, and/or software. Generally, the manner in which an optical communication system is implemented may vary, depending upon the particular application. The optical communication system 316 and other associated components are described in further detail below.

In a further aspect, balloon 300 may be configured for altitude control. For instance, balloon 300 may include a variable buoyancy system, which is configured to change the altitude of the balloon 300 by adjusting the volume and/or density of the gas in the balloon 300. A variable buoyancy system may take various forms, and may generally be any system that can change the volume and/or density of gas in the envelope 302.

In an example embodiment, a variable buoyancy system may include a bladder 310 that is located inside of envelope 302. The bladder 310 could be an elastic chamber configured to hold liquid and/or gas. Alternatively, the bladder 310 need not be inside the envelope 302. For instance, the bladder 310 could be a rigid bladder that could be pressurized well beyond neutral pressure. The buoyancy of the balloon 300 may therefore be adjusted by changing the density and/or volume of the gas in bladder 310. To change the density in bladder 310, balloon 300 may be configured with systems and/or mechanisms for heating and/or cooling the gas in bladder 310. Further, to change the volume, balloon 300 may include pumps or other features for adding gas to and/or removing gas from bladder 310. Additionally or alternatively, to change the volume of bladder 310, balloon 300 may include release valves or other features that are controllable to allow gas to escape from bladder 310. Multiple bladders 310 could be implemented within the scope of this disclosure. For instance, multiple bladders could be used to improve balloon stability.

In an example embodiment, the envelope 302 could be filled with helium, hydrogen or other lighter-than-air material. The envelope 302 could thus have an associated upward buoyancy force. In such an embodiment, air in the bladder 310 could be considered a ballast tank that may have an associated downward ballast force. In another example embodiment, the amount of air in the bladder 310 could be changed by pumping air (e.g., with an air compressor) into and out of the bladder 310. By adjusting the amount of air in the bladder 310, the ballast force may be controlled. In some embodiments, the ballast force may be used, in part, to counteract the buoyancy force and/or to provide altitude stability.

In other embodiments, the envelope 302 could be substantially rigid and include an enclosed volume. Air could be evacuated from envelope 302 while the enclosed volume is substantially maintained. In other words, at least a partial vacuum could be created and maintained within the enclosed volume. Thus, the envelope 302 and the enclosed volume could become lighter than air and provide a buoyancy force. In yet other embodiments, air or another material could be controllably introduced into the partial vacuum of the enclosed volume in an effort to adjust the overall buoyancy force and/or to provide altitude control.

In another embodiment, a portion of the envelope 302 could be a first color (e.g., black) and/or a first material from the rest of envelope 302, which may have a second color (e.g., white) and/or a second material. For instance, the first color and/or first material could be configured to absorb a relatively larger amount of solar energy than the second color and/or second material. Thus, rotating the balloon such that the first material is facing the sun may act to heat the envelope 302 as well as the gas inside the envelope 302. In this way, the buoyancy force of the envelope 302 may increase. By rotating the balloon such that the second material is facing the sun, the temperature of gas inside the envelope 302 may decrease. Accordingly, the buoyancy force may decrease. In this manner, the buoyancy force of the balloon could be adjusted by changing the temperature/volume of gas inside the envelope 302 using solar energy. In such embodiments, it is possible that a bladder 310 may not be a necessary element of balloon 300. Thus, in various contemplated embodiments, altitude control of balloon 300 could be achieved, at least in part, by adjusting the rotation of the balloon with respect to the sun.

Further, a balloon 306 may include a navigation system (not shown). The navigation system may implement station-keeping functions to maintain position within and/or move to a position in accordance with a desired topology. In particular, the navigation system may use altitudinal wind data to determine altitudinal adjustments that result in the wind carrying the balloon in a desired direction and/or to a desired location. The altitude-control system may then make adjustments to the density of the balloon chamber in order to effectuate the determined altitudinal adjustments and cause the balloon to move laterally to the desired direction and/or to the desired location. Alternatively, the altitudinal adjustments may be computed by a ground-based or satellite-based control system and communicated to the high-altitude balloon. In other embodiments, specific balloons in a heterogeneous balloon network may be configured to compute altitudinal adjustments for other balloons and transmit the adjustment commands to those other balloons.

As shown, the balloon 300 also includes a cut-down system 308. The cut-down system 308 may be activated to separate the payload 306 from the rest of balloon 300. The cut-down system 308 could include at least a connector, such as a balloon cord, connecting the payload 306 to the envelope 302 and a means for severing the connector (e.g., a shearing mechanism or an explosive bolt). In an example embodiment, the balloon cord, which may be nylon, is wrapped with a nichrome wire. A current could be passed through the nichrome wire to heat it and melt the cord, cutting the payload 306 away from the envelope 302.

The cut-down functionality may be utilized anytime the payload needs to be accessed on the ground, such as when it is time to remove balloon 300 from a balloon network, when maintenance is due on systems within payload 306, and/or when power supply 326 needs to be recharged or replaced.

In an alternative arrangement, a balloon may not include a cut-down system. In such an arrangement, the navigation system may be operable to navigate the balloon to a landing location, in the event the balloon needs to be removed from the network and/or accessed on the ground. Further, it is possible that a balloon may be self-sustaining, such that it does not need to be accessed on the ground. In yet other embodiments, in-flight balloons may be serviced by specific service balloons or another type of service aerostat or service aircraft.

3. Balloon Network with Optical and RF Links Between Balloons

In some embodiments, a high-altitude-balloon network may include super-node balloons, which communicate with one another via optical links, as well as sub-node balloons, which communicate with super-node balloons via RF links. Generally, the optical links between super-node balloons may be configured to have more bandwidth than the RF links between super-node and sub-node balloons. As such, the super-node balloons may function as the backbone of the balloon network, while the sub-nodes may provide sub-networks providing access to the balloon network and/or connecting the balloon network to other networks.

FIG. 4 is a simplified block diagram illustrating a balloon network that includes super-nodes and sub-nodes, according to an example embodiment. More specifically, FIG. 4 illustrates a portion of a balloon network 400 that includes super-node balloons 410A to 410C (which may also be referred to as “super-nodes”) and sub-node balloons 420 (which may also be referred to as “sub-nodes”).

Each super-node balloon 410A to 410C may include a free-space optical communication system that is operable for packet-data communication with other super-node balloons. As such, super-nodes may communicate with one another over optical links. For example, in the illustrated embodiment, super-node 410A and super-node 401B may communicate with one another over optical link 402, and super-node 410A and super-node 401C may communicate with one another over optical link 404.

Each of the sub-node balloons 420 may include a radio-frequency (RF) communication system that is operable for packet-data communication over one or more RF air interfaces. Accordingly, each super-node balloon 410A to 410C may include an RF communication system that is operable to route packet data to one or more nearby sub-node balloons 420. When a sub-node 420 receives packet data from a super-node 410, the sub-node 420 may use its RF communication system to route the packet data to a ground-based station 430 via an RF air interface.

As noted above, the super-nodes 410A to 410C may be configured for both longer-range optical communication with other super-nodes and shorter-range RF communications with nearby sub-nodes 420. For example, super-nodes 410A to 410C may use using high-power or ultra-bright LEDs to transmit optical signals over optical links 402, 404, which may extend for as much as 100 miles, or possibly more. Configured as such, the super-nodes 410A to 410C may be capable of optical communications at data rates of 10 to 50 GBit/sec or more.

A larger number of high-altitude balloons may then be configured as sub-nodes, which may communicate with ground-based Internet nodes at data rates on the order of approximately 10 Mbit/sec. For instance, in the illustrated implementation, the sub-nodes 420 may be configured to connect the super-nodes 410 to other networks and/or directly to client devices.

Note that the data speeds and link distances described in the above example and elsewhere herein are provided for illustrative purposes and should not be considered limiting; other data speeds and link distances are possible.

In some embodiments, the super-nodes 410A to 410C may function as a core network, while the sub-nodes 420 function as one or more access networks to the core network. In such an embodiment, some or all of the sub-nodes 420 may also function as gateways to the balloon network 400. Additionally or alternatively, some or all of ground-based stations 430 may function as gateways to the balloon network 400.

4. Thermal Regulation of the Balloon Payload with an Electronic Ink Covering on the Outer Surface of the Payload Structure that May Change the Energy Absorptive Properties of the Payload

As noted above, balloons may experience a wide range of environmental temperatures. For example, the balloon and its components may get very hot when positioned in bright sunlight during the day, and may get very cold during the night when the sun goes down. As a result, it may be desirable to maintain a narrower range of temperatures for the payload in view of the instruments and electronic equipment that may be located in the payload of the balloon. Thus, when the sun is at its brightest, the temperature of the payload may be effectively reduced by reflecting sunlight away from the payload of the balloon, which may be accomplished by providing a reflective surface on the payload, or a light-colored or white surface on the payload that does not absorb the sunlight.

However, near the end of the day, as the sun goes down, and less sunlight is directed toward the balloon and payload, it may be desirable to direct as much sunlight as possible into the payload. Thus, when the sunlight is low, the temperature of the payload may be effectively increased by allowing sunlight to enter the payload and heat the instruments and electronic devices within the payload, which may be accomplished by providing an energy absorptive surface on the payload, such as a dark-colored or black surface, and/or a transparent covering on the payload, that will allow the heat from the sunlight to be transferred into the payload.

Thus, in some circumstances it may be desirable to provide a payload having a reflective surface, or less energy absorptive surface, such as a light-colored, or white surface, while other times it may be desirable to provide a payload having an energy absorptive surface, such as a dark-colored, or black surface. Therefore, it may be desirable to have a payload that is capable of having the surface of the payload change from one having a reflective surface, or less energy absorptive surface, such as light-colored, or white surface, to one having an energy absorptive surface, such as a dark-colored, or black surface.

Example embodiments disclose a payload that has a surface that may change from an energy absorptive surface to an energy reflective surface. For example, the surface of the payload may be covered with an electronic ink covering that may be changed from a dark-colored, energy absorptive surface, to a light-colored, reflective, or less energy absorptive surface by applying a potential difference across electrodes associated with the electronic ink covering of the payload.

An example embodiment of a balloon payload having an electronic ink covering is shown in FIGS. 5 and 6. Balloon 20 is shown having a payload 30 positioned beneath the balloon 20 which may house various instruments and electronic devices. The payload 30 is shown in FIG. 5 with an electronic ink covering 32 shown in a first state, where the surface of the electronic ink covering 32 is shown as a dark-colored surface that absorbs the sunlight 530 from sun 540. In this manner, with the electronic ink covering 32 shown in a first state with a dark-colored surface, the thermal energy from the sunlight that is received by the payload is greater than if the surface of the electronic ink covering 32 was reflective or light-colored, and thus less energy absorptive.

Balloon 20 having payload 30 is shown in FIG. 6 with electronic ink covering 32 shown in a second state, where the surface of the electronic ink covering 32 is shown as a light-colored surface that reflects sunlight 530 (as shown in reflecting sun rays 530 a), or absorbs less sunlight than the dark-colored surface of electronic ink covering 32 shown in FIG. 5. Thus, when the electronic ink covering 32 is shown in a second state with a light-colored surface, the thermal energy from the sunlight that is received by the payload 30 is less than when the electronic ink covering 32 is in the first state with a dark-colored surface which is more energy absorptive.

Therefore, the electronic ink covering 32 may be caused to be in a first state with a dark-colored surface when it is desired to have an increased level of thermal energy from the sunlight entering the payload 30, and the electronic ink covering 32 may be caused to be in a second state with a light-colored surface when it is desired to have a lower level of thermal energy from the sunlight entering the payload. Thus, having the electronic ink covering 32 in a second state may be desirable during periods when the sun 540 is shining the brightest and helps to effectively reduce the temperature of payload 30 and its components.

Conversely, where it desired to increase the temperature of the payload 30, the electronic ink covering 30 may be caused to be in the first state with a dark-colored surface to absorb sunlight 530 for the payload 30 to effectively increase the temperature of the payload 30, and contents therein, if desired. As the sun goes down, and less sunlight 530 is directed toward the payload 30, it may be desirable to direct as much sunlight 530 as possible towards the payload 30. Thus, when the sunlight is low, the temperature of the payload 30 may be effectively increased by causing the electronic ink covering 30 to be in a first state with a dark-colored surface which will absorb more thermal energy from the sunlight 530. The electronic ink covering 32 may be changed back and forth between a first state and a second state as desired.

FIG. 7A shows a cross-section of the payload 30 of FIG. 5 taken along lines 7A-7A. In FIG. 7A, the electronic ink covering 32 is shown in a first state, with a dark-colored surface. FIG. 7B shows a cross-section of the payload 30 of FIG. 6 taken along lines 7B-7B. In FIG. 7B, the electronic ink covering 32 is shown in a second state, with a light-colored surface.

FIG. 8A shows an enlarged view of encircled portion 8A shown in FIG. 7A. Electronic ink covering 32 is shown positioned on the outside of payload 30. Microcapsules 40 are shown positioned between electrode 36 and electrode 38. Dark-colored particles 42 and light-colored particles 46 are shown positioned within dielectric fluid 48. When a potential difference between electrode 36 and electrode 38 is created, the dark-colored particles 42 migrate toward electrode 36 which is shown as positive in FIG. 8A, and the light-colored particles 46 migrate towards electrode 38 which is shown as negative in FIG. 8A. The dark-colored particles 42 provide a dark-colored surface for the electronic ink covering 32 in the first state and absorb thermal energy. The electrodes 36 and 38 may be transparent to allow sunlight to enter into payload 30.

FIG. 8B shows an enlarged view of encircled portion 8B shown in FIG. 7B. Electronic ink covering 32 is shown positioned on the outside of payload 30. Microcapsules 40 are shown positioned between electrode 36 and electrode 38. Dark-colored particles 42 and light-colored particles 46 are shown positioned within dielectric fluid 48. When a potential difference between electrode 36 and electrode 38 is created in this example, with electrode 36 positive and electrode 38 negative, the dark-colored particles 42 migrate toward electrode 38 and the light-colored particles 46 migrate towards electrode 36. The light-colored particles 46 provide a light-colored surface for the electronic ink covering 32 in the second state and absorb less thermal energy than the black particles.

As shown in FIGS. 8A and 8B, the size of the microcapsules 40 may be similar in diameter to the distance between electrodes 36 and 38. The microcapsules do not need to be spherical, but may range in size from 5 to 500 microns, although in an embodiment they range from 25 to 250 microns in size. The particles may range in size from 1-100 microns, although in an embodiment they range in size from 5-25 microns in size. It will be appreciated that some or all of the surface of the payload structure may be covered with an electronic ink covering. In addition, the electronic ink covering could be rigid or flexible, and could be a single contiguous covering, or it could be made of a number of separate electronic ink coverings, each which may have their own electrodes, that together make up the covering. Commercially available electronic ink displays are available from E Ink of Cambridge, Mass., USA.

In addition to using electronic ink on the surface of the balloon payload, passive changeable material could also be used on the surface of the balloon payload for purposes of thermal regulation. For example, there are materials that darken when exposed to the UV light and such a material might increase the absorption of the side of the payload facing the sun no matter how it was turned. Similarly, there are materials that become more reflective when exposed to UV light, and such a material might decrease the absorption of the side of the payload facing the sun no matter how it was turned. Also, the material might change properties depending on its temperature to, for example, let in more or less heat from the sun during the days (when the external temperature is much higher) or to increase or decrease the black-body radiation of the payload at night (when the external temperature is much lower). Thus, the balloon payload could use a passive mechanism that changes its energy absorptive properties based on exposure to UV light or temperature, as alternate to using an active mechanism like electronic ink.

As shown in FIGS. 9 and 10, electronic ink covering 32 may be positioned on the outer surface of payload 30, and microcapsules 60 are shown positioned between electrodes 56 and 58. When a potential is created between electrode 56 and electrode 58, the dark particles 62 within microcapsules 60 migrate towards electrode 56 which is shown as positive in FIG. 9. Similar to FIG. 8A, the dark-colored particles 62 provide a dark-colored surface for the electronic ink covering 32 in the first state and absorb thermal energy. FIG. 10 shows microcapsules 60 positioned between electrode 56 and electrode 58 when no potential is applied between the electrodes.

Alternately, or in addition, when the electronic ink cover 32 is in a first state and it is desired to increase the thermal energy directed towards the instruments and electronic equipment within the payload 30, a retractable mirror may be positioned on the balloon or payload that, when extended, directs sunlight onto the payload 30. A concave mirror may be positioned such that the payload is positioned at the focal point of the concave mirror. Conversely, when less thermal energy is desired to be directed into the payload 30, a retractable curtain could be placed around some or all of the payload to prevent sunlight from entering the payload 30.

With reference to FIG. 3, the electronic ink covering 32 of payload 30 could be controlled to cause the electronic ink covering be in a first state, or in a second state, and allow the electronic ink covering 32 to change back and forth between a first state and a second state as desired. Changing the electronic ink covering 32 from a first state to a second state, and vice-versa could be performed using processor 312 and memory 314 to control the state of the electronic ink covering 32. Alternatively, the state of the electronic ink covering 32 could be controlled remotely by another balloon or ground- or space-based station.

FIG. 11 shows a method 1200 that is provided that includes the step 1202 of causing a payload of a balloon to be placed in a first state wherein the payload includes a payload structure where the outer surface of the payload has an electronic ink covering, where in the first state, the electronic ink covering has first energy absorptive properties with respect to the amount of thermal energy from sunlight that enters the payload, and the step 1204 of causing the payload of the balloon to change to a second state, where in the second state, the electronic ink covering has second energy absorptive properties that allows less thermal energy from sunlight to enter the payload than the first state. The method 1200 may further include step 1206 of causing the causing the payload of the balloon to change back to the first state.

5. A Non-Transitory Computer Readable Medium with Instructions to Cause the Electronic Ink Cover to be in a First State or a Second State.

Some or all of the functions described above and illustrated in FIGS. 5-10 may be performed by a computing device in response to the execution of instructions stored in a non-transitory computer readable medium. The non-transitory computer readable medium could be, for example, a random access memory (RAM), a read-only memory (ROM), a flash memory, a cache memory, one or more magnetically encoded discs, one or more optically encoded discs, or any other form of non-transitory data storage. The non-transitory computer readable medium could also be distributed among multiple data storage elements, which could be remotely located from each other. The computing device that executes the stored instructions could be a computing device, such as the processor 312 illustrated in FIG. 3. Alternatively, the computing device that executes the stored instructions could be another computing device, such as a server in a server network, or a ground-based station.

The non-transitory computer readable medium may store instructions executable by the processor 312 to perform various functions. The functions could include causing the electronic ink cover to be in a first state, to be in a second state, or to change from a first state to a second state, and vice versa.

CONCLUSION

The above detailed description describes various features and functions of the disclosed systems, devices, and methods with reference to the accompanying figures. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 

What is claimed is:
 1. A balloon payload, comprising: a balloon payload structure attached to a balloon envelope; an outer surface of the balloon payload structure comprised of an electronic ink covering, and a control system configured to change the electronic ink covering from a first state having first energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, to a second state having second energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, wherein the second energy absorptive properties allow less thermal energy to enter the payload than the first energy absorptive properties.
 2. The balloon payload of claim 1, wherein the electronic ink covering is comprised of an electrophoretic display.
 3. The balloon payload of claim 1, wherein the first state of the electronic ink covering provides a dark-colored surface on the electronic ink covering, and the second state of the electronic ink covering provides a light-colored surface on the electronic ink covering.
 4. The balloon payload of claim 3, wherein the dark-colored surface on the electronic ink covering in the first state allows more solar energy to be absorbed by the payload than when the electronic ink covering is in the second state.
 5. The balloon payload of claim 1, wherein the electronic ink covering includes a first electrode and a second electrode with dielectric fluid and a suspension of particles positioned between the first and second electrodes.
 6. The balloon payload of claim 5, wherein the particles visually contrast with the dielectric fluid, and wherein the control system is configured to create a potential between the first electrode and the second electrode, such that the particles are caused to migrate toward one of the electrodes.
 7. The balloon payload of claim 5, wherein microcapsules are positioned between the electrodes and dielectric fluid and particles are positioned within the microcapsules.
 8. The balloon payload of claim 6, wherein the particles are dark-colored, and when the potential between the first electrode and second electrode is created, the dark-colored particles migrate towards the electrode on the outer surface of the electronic ink covering to create the first state.
 9. The balloon payload of claim 7, wherein the particles within the microcapsules are dark-colored, and when the potential between the first electrode and second electrode is created, the dark-colored particles migrate towards the electrode on the outer surface of the electronic ink covering to create the first state.
 10. The balloon payload of claim 1, wherein the change from the first state to the second state is caused when a predetermined temperature is detected within the payload.
 11. The balloon payload of claim 1, wherein the payload is secured beneath the balloon envelope when the balloon envelope is aloft.
 12. A balloon payload, comprising: a balloon payload structure; an outer surface of the balloon payload structure comprised of an electronic ink covering, and a control system configured to change the electronic ink covering from a first state having first energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, to a second state having second energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, wherein the second energy absorptive properties allow more thermal energy to enter the payload than the first energy absorptive properties; wherein the balloon payload structure is carried beneath a balloon envelope adapted to be filled with a lifting gas.
 13. A computer-implemented method, comprising: causing a payload of a balloon to be placed in a first state wherein the payload includes a payload structure where an outer surface of the payload structure is comprised of an electronic ink covering, where in the first state, the electronic ink covering has first energy absorptive properties with respect to the thermal energy that enters the payload through the electronic ink covering, causing the payload of the balloon to change to a second state, where in the second state, the electronic ink covering has second energy absorptive properties that allow less thermal energy to enter the payload than when the electronic ink covering is in the first state.
 14. The computer-implemented method of claim 13, wherein the electronic ink covering is comprised of an electrophoretic display.
 15. The computer-implemented method of claim 13, wherein the first state of the electronic ink covering provides a dark-colored surface on the electronic ink covering, and the second state of the electronic ink covering provides a light-colored surface on the electronic ink covering.
 16. The computer-implemented method of claim 13, wherein the electronic ink covering includes a first electrode and a second electrode with dielectric fluid and a suspension of particles positioned between the first and second electrodes.
 17. The computer-implemented method of claim 16, wherein the particles visually contrast with the dielectric fluid, and wherein a potential is created between the first electrode and the second electrode, such that the particles are caused to migrate toward one of the electrodes.
 18. The computer-implemented method of claim 17, wherein the particles are dark-colored, and when the potential between the first electrode and second electrode is created, the dark-colored particles migrate towards the electrode on the outer surface of the electronic ink covering to create the first state.
 19. The computer-implemented method of claim 13, further including causing the payload of the balloon to change back to the first state.
 20. The computer-implemented method of claim 13, wherein the change from the first state to the second state is caused when a predetermined temperature is detected within the payload.
 21. A non-transitory computer readable medium having stored therein instructions executable by a computing device to cause the computing device to perform functions comprising: causing a payload of a balloon to be placed in a first state wherein the payload includes a payload structure where an outer surface of the payload structure is comprised of an electronic ink covering, where in the first state, the electronic ink covering has first energy absorptive properties with respect to thermal energy that enters the payload through the electronic ink covering, causing the payload of the balloon to change to a second state, where in the second state, the electronic ink covering has second energy absorptive properties that allow less thermal energy to enter the payload through the electronic ink covering than when the electronic ink covering is in the first state.
 22. The non-transitory computer readable medium of claim 21, wherein the electronic ink covering is comprised of an electrophoretic display.
 23. The non-transitory computer readable medium of claim 21, wherein the first state of the electronic ink covering provides a dark-colored surface on the electronic ink covering, and the second state of the electronic ink covering provides a light-colored surface on the electronic ink covering.
 24. The non-transitory computer readable medium of claim 21, wherein the electronic ink covering includes a first electrode and a second electrode with dielectric fluid and a suspension of particles positioned between the first and second electrodes.
 25. The non-transitory computer readable medium of claim 24, wherein the particles visually contrast with the dielectric fluid, and wherein the control system is configured to create a potential between the first electrode and the second electrode, such that the particles are caused to migrate toward one of the electrodes.
 26. The non-transitory computer readable medium of claim 25, wherein the particles are dark-colored, and when the potential between the first electrode and second electrode is created, the dark-colored particles migrate towards the electrode on the outer surface of the electronic ink covering to create the first state. 